FIELD OF THE INVENTION

This invention relates to the field of actuators. More specifically this invention

relates to a continuous rotary or linear actuator utilizing shape memory alloy material for

continuous rotary power

BACKGROUND OF THE INVENTION

One widely known and used type of actuator is the electric motor, Electric

motors are used universally used in industry. They can be found in many devices ranging

from refrigerators to hair dryers to vehicles. An electric motor depends on magnetism to

create motion. The attracting and repelling poles of a magnet create rotational motion to

power the actuator, A commutator allows for the flipping of the field to keep the force

moving. The magnets are paired with a power supply to create an electromagnet force

powering the motors motion.

Another type of actuator is the stepper motor. Stepper motors are commonly used

in the office setting as they are found in computer peripherals, such as the printer;

business machines, such as a copy machine or a card reader; process controls, such as a

conveyor system; and in machine tools, such as a laser cutter. Stepper motors may

simply be seen as an electric motor without the commutator. These motors seem to

function best at low accelerations and a static load, such as what is seen in a copy

machine settings as the paper moves through the system at a low, constant speed and

load.

In many industries, there is a need for miniaturization of motors/actuators that

have reduced size, mass, power consumption, and cost. Traditional actuators include

electromechanical, pneumatic, or hydraulic systems. However, using these systems for

applications requiring small actuators is not always the best option as these systems are

often times too large, heavy, expensive, or energy wasting. Attempts at miniaturizing

existing actuator systems, including the use of SMA, have resulted in more expensive and

yet iess efficient systems. As a result, there is a need for more advanced actuator systems

for current technologies of smaller sizes.

Typical SMA actuators do not provide continuous/stepping rotary or linear

motion. Current industrial applications of SMA include valves, clamping devices,

fasteners, and linear actuators. These examples typically have only two positions

corresponding with an "on" and "off state - they do not have the capability of providing

continuous/stepping motion in one or more directions. This limits practical uses of SMA.

However, this invention will be capable of providing continuous/stepping rotary or linear

motion similar to the ubiquitous electric actuator.

In contrast to conventional actuators, SMA actuators increase efficiency as they

decrease in size, It has been proved that when comparing several actuating technologies

(from small DC actuators to gas turbines) the SMA actuators offer the highest

power/weight ratio at low weights (below 100 grams). Thus, the invention of an SMA

actuator capable of continuous/stepping rotary or linear motion may have significant

practical applications in industries requiring miniature actuators including medicine,

defense, aerospace, and micro and nanotechnology to name a few.

SUMMARY OF THE INVENTION

This invention represents and fundamental paradigm shift away from traditional

actuator systems. This invention is an application of smart memory alloy (SMA) for

continuous/stepping rotary or linear power. What is claimed is:

A continuous/stepping rotary or linear actuator comprising:

a rotating output shaft;

an drive gear;

at least one means for rotating said drive gear comprising material adapted

to contract when activated; and

electronic control.

The means for rotating said drive gear further comprises a pawl, a shuttle, a

shuttle capture, a spring anchor, and a spring. This means for rotating said drive gear

utilize power and motion generated by material adapted to contract when activated.

When the material adapted to contract is activated, it moves the shuttle and pawl in a

desired manner. Upon this movement, the pawl grasps and turns the drive gear which is

coupled to the output shaft. λ spring is used to return the shuttle and pawl back to a start

position to repeat the cycle.

In some preferments, the material adapted to contract when activated is simply a

strip that contracts to move the pawl. In a more compact setting, the material adapted to

contract when activated is wound through an accumulator. The material adapted to

contract is activated and will contract through this accumulator causing movement of the

drive gear and thereby rotating the output shaft.

The material adapted to contract when activated is preferably shape memory alloy

strip, wire or other form. Shape memory alloys are known and are usually made

predominantly or wholly of titanium and nickel. They may also include other material,

such as aluminium, zinc copper, and other similar materials. A shape memory alloy is

capable of adopting one shape below a predetermined transition temperature and

changing to a second shape once its temperature exceeds the transition temperature.

Conversely, when the shape memory alloy cools below the transition temperature, it is

capable of adopting the first shape again. In connection with the present invention, the

shape memory alloy preferably contracts when heated in situ. Shape memory alloy strip

and wire currently available, such as that sold under the trade mark Nitinol, is capable of

contracting for many cycles by about 3% when activated by heating.

Activation of the material adapted to contract when activated is preferably

achieved through electrical resistance heating, with a wire feed to the assembly.

Activation of the shape memory alloy strip can be initiated from a central location, using

the wiring system of, for example, an aircraft or automobile. It is also within the scope

of this invention that the activation is initiated by remote means, such as a hand held tool

operating through the use of any suitable form of energy, including microwave, electric

magnetic, sonic, infra-red, radio frequency and so on.

The scope of the invention is not necessarily limited to the use of shape memory

alloy. Other material may also be useful, such as such as shape memory polymers,

electro or magneto restrictive materials or piezo electric materials. Also, while activation

may take place through heating, other means of activation may be suitable and are within

the scope of this invention.

As discussed above, the actuator can provide continuous or stepped motion. The

means for rotating said drive gear can operate in a variety of modes. Three known modes

are the high torque mode, endurance mode, and the speed mode. The high torque mode

is to be used when the continuous/stepping rotary actuator is needed to generate higher

torque. The high torque mode is achieved by increasing the number of SMA elements or

wires turning the gear at any one time, so that the force applied by the SMA elements add

together. The endurance mode can be achieved by decreasing the cycles for each SMA

element. The decrease in cycles will increase the overall lifespan on the

continuous/stepping rotary or linear actuator. The strips then have time to cool in

between cycles. The speed mode can be achieved when one SMA strip or wire is

energized sequentially in order to increase the cooling time in between cycles of the

individual strip. For example, when one strip is heated to drive the mechanism, one or

more previously heated strips are cooling at the same time reading themselves for their

next heating cycle. In this mode, only one strip is activated at any given time. The same

principles apply to other types of drive elements which have a limitation on their

maximum cycle rate.

Should an SMA element fail or break, it may simply be taken out of the activation

sequence. Thus, the actuator may have an ability to self heal by compensating for non¬

functional SMA elements by recruiting functional SMA elements. The mechanism has

built-in redundancy.

The mechanism will function with a simple drive circuit and control strategy,

which sequentially activates the drive gear in the required combination and sequence for

each mode of operation. However, performance can be greatly enhanced by the use of an

intelligent multi-channel control circuit such as a microcontroller based module which

provides accurate, flexible control of mechanism operation.

In order to enhance the performance of the mechanism, sensing is incorporated to

allow the position of each drive gear to be determined. This allows accurate

determination of the drive gear position, so that only just the right amount of energy must

be applied to cause the element to heat and contract by only the required amount. The

return of the drive gear to the position ready for its next cycle can also be detected. This

will allow cycle time to be minimized and the cycle rate maximized. Correspondingly,

energy consumption can be minimized and efficiency maximized.

Sensors also allow the operation of each drive gear to be monitored, allowing

failed drive gears to be identified and the control strategy adjusted to avoid use of the

failed element.

The continuous/stepping rotary or linear actuator may also function with the drive

gear and at least one means for rotating the drive gear in a stacked position. Stacking

allows the actuator to perform a variety of desired functions. Stacking allows for

bidirectional motion (forward and reverse) and allows for increased torque and precision

stepping control. As such the continuous/stepping rotary or linear actuator comprises:

a rotating output shaft;

more then one drive gear;

more then one means for rotating said drive gears comprising material

adapted to contract when activated; and

electronic control.

The continuous/stepping rotary actuator parts function in substantially the same

manner stacked as they do in a single arrangement. Stacking simply provides some

added advantages.

When stacking is used in a bidirectional motion, one or more drive gears are set

for clockwise motion along with one or more drive gears set for counterclockwise

motion.

Stacking is instrumental in achieving reduced angular movement. The stacking

will allow for more precision control. As the drive gears and the means for rotating the

drive gears are stacked, fine graduation is achieved by the incremental positioning along

the output shaft. If the first drive gear is can be moved a certain angle, then the next

stacked drive gear will reduce the angle position by 50% and the next stacked drive gear

will reduce it by another 50% so that exact precision can be achieved. The stacking can

be repeated any number of times to achieve the most angular precision needed by an

application.

Stacking will also allow for more torque, endurance, speed, or indexing in the

varying modes as described above.

This continuous/stepping rotary or linear actuator may also be useful in a fastener

setting. Using the invention allows for fasteners to be self-tightening and self-loosening.

An obvious application of this would be as adapted to a screw type fastener. This self-

tightening feature may also be combined with a clutch feature to tighten itself to a

specific torque.

An important and unique feature of this invention is that it is not subject to

magnetic fields as typical electric actuators are. As such, this continuous/stepping rotary

or linear actuator can be used in magnetic settings without interference.

Unlike conventional actuators, this invention has silent actuation which is

advantageous in many settings.

Also unlike conventional actuators, this invention can be made extremely thin. In

the most compact setting where the accumulator has wound the SMA strips or wire, this

invention can be used in a computer setting or other setting where miniature actuators arc

desired.

Other advantages and aspects of the present invention will become apparent upon

reading the following description of the drawings and the detailed description of a

preferred embodiment of the invention.

DETAILED DESCRIPTION OF THE DRAWINGS

FIG. 1 depicts an exploded view of the continuous/stepping rotary actuator

utilizing an accumulator.

FIG. 2 depicts the means for rotating the drive gear, including the material

adapted to contract when activated.

FIG. 3 depicts an exploded view of the means for rotating the drive gear,

including the material adapted to contract when activated.

FIG. 4 depicts a unidirectional continuous/stepping rotary actuator.

FIG. 5 depicts a bidirectional continuous/stepping rotary actuator.

FIG. 6 depicts the continuous/stepping rotary actuator in the high torque mode.

FIG. 6A depicts the combination of the means for rotating the drive gear,

including the material adapted to contract when activated with the corresponding angular

position of the continuous/stepping rotary actuator in achieving the high torque mode.

FIG. 7 depicts the continuous/stepping rotary actuator in the endurance mode.

FIG. 7A depicts the combination of the means for rotating the drive gear,

including the material adapted to contract when activated with the corresponding angular

position of the continuous/stepping rotary actuator in achieving the endurance mode.

FIG. 8 depicts the continuous/stepping rotary actuator in the speed mode.

FIG. 8 A depicts the combination of the means for rotating the drive gear,

including the material adapted to contract when activated with the corresponding angular

position of the continuous/stepping rotary actuator in achieving the speed mode.

FIG. 9 depicts a linear embodiment of the continuous/stepping actuator.

FIG. 10 depicts an exploded view of the linear embodiment of the

continuous/stepping rotary actuator,

FIG. 1 1 depicts a linear embodiment of the continuous/stepping actuator.

FIG. 12 depicts an exploded view of the linear embodiment of the

continuous/stepping actuator.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

This invention relates to a continuous/stepping rotary or linear actuator

comprising a rotating output shaft 4, a drive gear 10, and at least one means for rotating

12 the drive gear 10 comprising material adapted to contract when activated 14, and

electronic controls 30,

The means for rotating 12 the drive gear 10 further comprises a pawl 16, a shuttle

24, and a spring 22. This means for rotating 12 said drive gear 10 utilize force and

motion generated by material adapted to contract 14 when activated. When the material

adapted to contract 14 is activated, it moves the shuttle 24 and pawl 16 in a desired

manner. Upon this movement, the pawl 16 grasps and turns drive gear 10 which drives

the motion of the output shaft 4.

FIG. 2 and 3 depict detailed illustrations of the means for rotating the drive gear

10 comprising the pawl 16, shuttle 24, shuttle capture 18, spring anchor 20, and spring

22. Also seen is the material adapted to contract 14 when activated. The material

adapted to contract 14 is preferably a SMA strip or wire.

The spring 22 simply assists in bringing the material adapted to contract 14 back

to its pre-activation setting. The spring anchor 20 simply holds the pawl 16, shuttle 24,

and shuttle capture 18 in place.

FIGS. 4 and 5 depict a setting whereby the material adapted to contract 14 is in

single straight strips. Another preferment is seen in FIG. 1 whereby the material adapted

to contract 14 is wound about an accumulator 6. The embodiment utilizing the

accumulator 6, is for a more tight, compact setting that still desires the full activation of

the material adapted to contract 14.

This invention may also comprise a print circuit board (PCB) 26. The PCB

provides a means to make electrical connections. Many of the internal components may

be integrated into the PCB,

This continuous/stepping actuator can operate as a unidirectional unit as seen in

FIG. 4 or a bidirectional unit as seen in FIG. 5. When operating as a unidirectional unit,

the continuous/stepping rotary actuator only moves in one direction. When operating as a

bidirectional unit, the continuous/stepping rotary actuator can operate in a forward or

reverse manner.

The continuous/stepping actuator operates in a bidirectional manner, this is due to

another preferred embodiment comprising more then one drive gears 10 and more then

one means for rotating 12 drive gears 10 which all work to turn the output shaft 4. This is

called stacking. Stacking can result not only in bidirectional movement, but increased

torque, endurance, speed, and indexing, precision control and fine graduation of angular

positioning. The parts involved in a stacked setting simply perform as they would in a

non-stacked setting but offer added advantages as realized above.

This continuous/stepping rotary actuator can operate in various modes. Three

known modes are the high torque mode (FIG. 6 and 6A), endurance mode (FIG 7 and

7A), and the speed mode (FIG. 8 and 8A). One skilled in the art will recognize that other

modes may be possible. The high torque mode is to be used when the

continuous/stepping rotary actuator is needed to generate more torque. The high torque

mode is achieved by increasing the number of means for rotating drive gear 10 at any one

time. As seen in Figure 6A, there are eight means for driving the driving gear 10. At any

given time, half of the means for rotating the drive gears 10 (in this case four) are

operating at once. Once those four have been activated, they deactivate to let the other

four activate and continue to move the drive gear 10 to rotate the output shaft 4. Other

combinations of drive gear 10 activation are possible. The endurance mode can be

achieved by decreasing the cycles for each means of rotating driving gear 10. This

decrease in cycles will increase the overall lifespan on the continuous/stepping rotary

actuator because the material adapted to contract 14 when activated will then have time to

cool in between cycles. As seen in Fig 7A, at any given time only two means of rotating

the out put shaft 12 are operating at once. The remaining means of rotating the out put

shaft 12 are at rest and cooling so that the lifespan of the material adapted to contract 14

will have a longer lifespan. The speed mode can be achieved when the means of rotating

the out put shaft 12 are energized sequentially in order to increase the cooling time in

between cycles of the individual strip of material adapted to contract 14. As seen in FIG.

SA, only one strip is activated at any given time. By increasing the time allowed for

cooling of each individual strip of material adapted to contract 14, the

continuous/stepping rotary actuator can increase its frequency.

Other embodiments of the continuous/stepping actuator are seen in FIGS. 9-12.

FIGS. 9 and 10 detail a cylindrical linear form of this invention while FIGS. 1 1 and 12

details another linear embodiment. These alternative embodiments perform in

substantially the same manner as the actuators discussed above. FIG. 12 details an

overstress spring 32 that can be added to this invention to prevent an ovcrstress situation

of the material adapted to contract 14.

The invention may be described in terms of claims that can assist the skilled

reader in understanding the various aspects and preferments of the invention. It will be

appreciated by those skilled in the art that many modifications and variations may be

made to the embodiments described herein without departing from the spirit and scope of

the invention.

Industrial Applicability

As will be appreciated by those skilled in the various arts, this invention disclosed

herein is not limited to the examples set our above and has wide application in many

areas. This invention represents a significant advance in the art of actuators.